Flexible radio frequency transmission line



Dec. 23, 1941. E. GERHARU 2,267,455 FLEXIBLE RADIO FREQUENCY TRANSMISSIUN LINE Filed July 18, 1939 INVENTOR ERNST GERHA RD ATTORNEY Patented Dec. 23, 1941 FLEXIBLE RADIO FREQUENCY TRANSMISSION LINE Ernst Gerhard, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application July 18, 1939, Serial No. 285,088 In Germany August 2, 1938 6 Claims.

For commercial and technological purposes there are frequent demands for flexible radio frequency feeder leads or transmission lines which are of ample cross-sectional area and possess a large conductor surface. But certain difficulties are encountered in the attempt at making such leads or lines of adequate flexibility. The use of Litz wire or strand or of wrapped or wound hollow cables of the kind used, for instance, in high potential work would not be possible for radio frequency work. Also known in the prior art are co-axial or concentric radio frequency lines or cables which consist of a flexible interior conductor and of an outer conductor surrounding the former and consisting of a plurality of elastically or flexibly connected meshes or links. However, structures of this nature are of comparatively complex construction.

Radio frequency leads or lines are also known in the art which consists of two bandor tapeshaped parallel conductors, the two conductors being separated and spaced apart by suitable insulators. While it is true that such a line possessesfiexibility in the direction at right angles to the surface of the band or ribbon, it involves the drawback that when the cable is wound upon a drum or the like, or when the cable is laid in a curved or arcuate position, the two bands are shifted in relation to each other; hence, the spacing means can not be fixedly attached to the cable bands lest an unduly high mechanical strain or stress arise therein. But if they were mounted loosely, there would be no assurance that the spacer means would remain uniformly spaced apart along the cable whenever the latter is subject to repeated to-and-fro bending, for instance, as a result of winding the cable on the drum and paying it out therefrom several times. Another point is that the insulators would be subject to far more intense heating because of the poorer contact between the insulators and the radio frequency carrying ribbons or bands of the cable.

According to the invention the radio frequency energy feeder or transmission line consists of two parallel metallic bands which are twisted about their common longitudinal axis of symmetry, with the spacers being disposed at distances from one another equal to the pitch of the twist.

The arrangement of the bands is schematically illustrated ln Figure 1, while Figures 2 and 3 show end and side sectional views of the insuinside a full pitch of the twist. This results in the relative position of the bands at the particular point of the spacers being unaltered and therefore no mechanical stresses are'applied to the insulators due to shifting of the bands.

Figures 2 and 3 illustrate a preferred form of spacer of the kind usable for a cable as here disclosed. The spacer comprises a pair of arcuate insulating members 4 and 5 having opposing but spaced flat faces. Small grooves l and 5' are provided in each of the fiat faces of insulating members 4 and 5 for accommodating the two metallic bands I and 2. These slots or notches need to be of a depth of only a few millimetersin order to afford perfectly safe holding of the metallic bands. The two parts indicated at 4 and 5 comprising each of the spacers are locked together by a metallic ring 6 shown in plan in Figure 2 and in transverse section in Figure 3. This ring is preferably elastic and is laid into a slot extending around the circumference of the are pieces.

The cable built as hereinbefore specified may be confined inside a hose '1 made of insulating material, as shown in Fig. 2. The outer protecting hose 1 has not been shown in Fig. 3 for the sake of simplicity of disclosure. If desired, this hose 7 may be fitted exteriorly with the metallic shield or armor, though this is not shown in the drawing for the sake of greater clearness of illustration.

The invention is not confined to the embodiments here merely shown and described by way of example. In addition, it may be found advantageous to mount accessory spacers capable of a certain amount of shift or mobility between the main spacers fixedly disposed on the metallic bands one pitch apart.

I claim:

1. A flexible radio frequency transmission line comprising a pair of ribbon conductors having their flat surfaces parallel, said conductors being twisted about their longitudinal axis of symmetry and supported within a protective casing, said conductors being supported in position within said casing along their edges only.

2. A flexible radio frequency transmission line comprising a pair of ribbon conductors having their flat surfaces parallel and twisted about their longitudinal axis 'of symmetry, said conductors being supported in position by insulators having the form of a sector of a circle having shallow notches in their chords adapted to receive the edges of said ribbon conductors, the depth of said notches being substantially less than half the width of said ribbon conductors whereby a minimum of solid insulating material is interposed between said conductors.

3. A flexible radio frequency transmission line comprising a pair of parallel ribbon conductors twisted about their longitudinal axis of symmetry and supported within a protective casing, said conductors being supported in position within said casing along their edges only.

4. A flexible radio frequency transmission line comprising a pair ofvparallel ribbon conductors twisted about their longitudinal axis of symmetry and supported within a protective casing, said conductors being supported in position within said casing by insulators spaced from one another a distance equal to the pitch of the spiral.

5. A flexible radio frequency transmission line comprising a pair of parallel ribbon conductors twisted about their longitudinal axis of symmetry, and supported within a protective casing, said conductors being supported in position by insulators having the form of a sector of a circle having shallow notches in their chords adapted to receive the edges of said ribbon conductors, the depth of said notches being substantially less than half of the width of said ribbon conductors whereby a minimum of solid insulating material is interposed between said conductors.

6. A flexible radio frequency transmission line comprising a pair of parallel ribbon conductors twisted about their longitudinal axis of symmetry, and supported within a protective casing, said conductors being supported in position within said casing by insulators having the form of a sector of a circle less than a semi-circle and having shallow notches in their chords adapted -to receive the edges of said ribbon conductors whereby a minimum of solid insulating material is interposed between said conductors.

. ERNST GERHARD. 

